The invention relates to a composite speaker system, and more particularly to a composite speaker system of the type in which a low-range speaker unit is mounted flush with a rear parcel shelf of an automotive vehicle so that the open surface of the low-range speaker unit is directed upward.
If a conventional coaxial type composite speaker system, for example, a tri-axial speaker, is used in an automotive vehicle and is flush mounted on the rear parcel shelf, low-range, medium-range and high-range sounds emanating from the speaker system are reflected by the inside surface of the rear window of the vehicle. This type of conventional composite speaker is advantageous in that high fidelity low-range sound is well reproduced since the trunk serves as a cabinet for the speaker system and the space defined by the rear parcel shelf and the rear window serves as a horn. It is, however, disadvantageous in that sound waves of the medium-range and high-range sounds, which are the more important components for creating a stereophonic effect, are attenuated as a result of being reflected by the rear window.
This can be seen from the graph of FIG. 1 which indicates frequency versus sound pressure characteristic curves of a composite speaker system flush mounted on the rear parcel shelf of an automotive vehicle. The solid line I is a sound pressure characteristic curve of the medium-range and high-range sounds in the case of no reflection on the rear glass while the dotted line II illustrates the case of reflection. The conventional system is further disadvantageous in that the position of the sound image is not definite.